In a mobile communication system, a wired or wireless repeater is used to extend coverage of a base station. Further, intensity of a signal received from the base station to the repeater may vary over time. In other words, the intensity of the signal received from the base station to the repeater may vary according to the number of serviced communication terminals, an amount of transmitted traffic, or channel fading. Also, in general, the repeater generally transfers constant transmission power regardless of the intensity of the signal received from the base station. FIG. 1 illustrates a general mobile communication system including a base station, a repeater, and a terminal.
The repeater has a constant range in which communication is possible, which is called coverage. From the viewpoint of cell planning, it is a very important matter to maintain constant coverage of the repeater. In other words, there are problems in that communication quality is degraded due to interference between adjacent coverage when the coverage of the repeater becomes wide, and an area in which service is impossible is generated when the coverage becomes narrow. The coverage of the repeater may be changed in a predetermined range (between coverage 1 and coverage 2), as illustrated in FIG. 2. FIG. 2 is a schematic diagram illustrating a change in the coverage of the repeater.
Further, the coverage is actually determined based on intensity of a specific signal (e.g., a pilot signal) rather than total signal intensity. Therefore, there is a problem in that the constant coverage of the repeater cannot be maintained even when the repeater maintains constant transmission power.
In other words, a scheme for maintaining the constant coverage of the repeater is required for such a reason.
A conventional technology proposed to solve such a problem (Korean Patent Laid-open Publication No. 10-2006-0084761) is characterized in that coverage of a repeater is regulated through tracking of a pilot signal. However, there is a problem in that this conventional technology is restrictively applied to only a CDMA signal. In other words, the pilot signal is divided as a code in the CDMA signal, and it is not problematic to detect intensity of the pilot signal in the repeater.
However, in an orthogonal frequency division multiplexing (OFDM) technology, that is, an orthogonal frequency division multiplexing system, pilots are scattered on time/frequency and thus high complexity is required to detect a pilot signal. FIG. 3 is a graph illustrating a pilot structure in an OFDM system. In the graph illustrated in FIG. 3, a horizontal axis indicates time, a vertical axis indicates a frequency, and RO indicates the pilot signal.
In other words, in the case of LTE that is an OFDM-based system, a position in a frequency domain of a reference signal serving as the pilot signal is changed according to a subframe number and a base station ID unlike a conventional technology. Accordingly, an additional apparatus for searching for the position of the pilot (reference) is required.